Islamic State of Iraq and Syria fighters march in Syria

Fighters from the Islamic State of Iraq and Syria march in Raqqah, Syria, in this image from a militant-linked website. Al Qaeda's central command has declared that the group known as ISIS is not affiliated with Al Qaeda. (February 3, 2014)

BEIRUT — The general command of Al Qaeda has disavowed one of its best-known and most successful affiliates, the Islamic State of Iraq and Syria, which is waging a brutal guerrilla war in both Middle Eastern nations.

Apparently angered by the group's growing power and autonomy, Al Qaeda's Pakistani-based central command issued a blunt statement saying that the Islamic State is "not a branch of Al Qaeda," has no "organizational relationship" with Al Qaeda and its actions cannot be linked to Al Qaeda. The statement was posted on several militant websites early Monday.

Not only did Al Qaeda not endorse the Islamic State's creation, the statement said, but it also previously ordered the group to cease operations, without success. It complained that the group was wrongly targeting fellow Muslims who did not support it.

Today, the Islamic State, also known as ISIS, boasts a territorial influence that stretches from Anbar province in Iraq to the rebel-held stretches of northern Syria. Its ranks in Syria are reported to include thousands of non-Syrians, among them other Arab nationals, Europeans and Russians who have flocked to Syria to wage "jihad." The Islamic State's trademark weapon is the suicide car bomb.

The public rebuke came after months of friction between Al Qaeda's leadership and the Islamic State. The latter spun off from the former Islamic State of Iraq, which was established as the terrorist network's franchise in Iraq. In April 2013, the Islamic State of Iraq and Syria declared its birth, saying it had merged with a militant faction known as Al Nusra Front. That faction had gained notoriety for its car bomb attacks in Syria.

But Al Nusra Front officials and Al Qaeda's leader, Ayman Zawahiri, rejected the merger as a power play.

Since then, the Islamic State has earned a reputation for targeting other rebel groups it accuses of apostasy, implementing its extreme interpretation of Islam in the areas it controls and abusing civilian supporters of the opposition.

The Al Qaeda statement reflected its "attempt to definitively reassert some level of authority over the jihad in Syria," said Charles Lister of the Brookings Doha Center, who was quoted by the Associated Press. However, he said he doubted the Islamic State would back down and stop attacking rival factions.

Last month, fierce fighting broke out in Syria between the Islamic State and a new rebel alliance that included Al Nusra Front. Several hundred people have reportedly died in the rebel infighting, which continues in some parts of Syria.

The Islamic State was subsequently pushed out of a number of areas but continues to hold ground throughout northern Syria and is a major power broker in the northeastern rebel stronghold of Raqqah, the first Syrian provincial capital to fall completely into rebel hands.

Sandels is a special correspondent. Times staff writer Patrick J. McDonnell and special correspondent Nabih Bulos in Damascus, Syria, contributed to this report.